Another thing you can check is the adjuster itself. I had a ticking sound on #3 cylinder that I played with for years after I rebuilt my engine. I had adjusted the valves several times the standard way to no avail. I looked for an exhaust leak but could not find one. When I had the engine out for a clutch change I decided to investigate the rockers on this cylinder. I removed the intake and exhaust rocker shafts to inspect for wear. They were fine, no visible wear. The rockers fit the shafts correctly, no looseness so the bushing were OK. The only thing I could see was that one swivel cup of the adjuster on the exhaust side rocker arm was much looser than the intake. It made a clicking noise checking the cup for up/down slop. So, I bought a couple of new adjusters (expensive for what they are). I only needed one, but it was good that I bought two because one of the "new" ones was as loose as the old one. Anyway, I replaced the adjuster with a good one and adjusted the valves using the "backside" method. Now the tick is gone, the cylinder sounds the same as the others. I think the new adjuster and adjusting the valves using the "backside" method fixed this for me. Not saying this will fix your problem, but it is worth looking at.